This invention relates to range and angle location systems such as radar, and more particularly to such systems in which monopulse techniques are used to determine the location of targets, and in which a source of jamming signals is located at an angle near that of the target.
Radar systems use a transmitting antenna to transmit signals toward a target, and use a receiving antenna to receive echo signals reflected from the target. The receiving antenna may be collocated with the transmitting antenna, or it may be at a different location. When collocated, portions of the antenna structure may be common to both the transmitting and receiving functions. Early radar systems depended upon the use of a narrow beamwidth receiving antenna beams to aid in determining the actual azimuth of the target. Extremely narrow receiving beams tend to limit the scan rate of the system, because the receive beam must dwell at each angle for a sufficiently long time to receive an identifiable echo. A more modern scheme for determining the target azimuth angle uses monopulse techniques, in which sum and difference signals are generated from the received antenna signal. The sum signal corresponds to a conventional single-lobe beam, while the difference signal includes an on-axis null, so that a predetermined ratio of sum- and difference-beam amplitudes can be used, when near the sum-beam axis, to determine the off-axis angle. The difference pattern has a 180.degree. mutual phase shift between its adjacent lobes, and the side (left, right or up, down) of the central or boresight axis on which the target resides can be determined from the phase shift. This monopulse scheme is highly effective and widely used.
Numerous schemes have been used to suppress or reduce the effects of interference or intentional jamming of radar systems. Sidelobe cancelers of various types are well known. Copending patent application Ser. No. 07/644,358, filed Jan. 22, 1991 in the name of Kott, describes an arrangement for nulling the beam of an array antenna to reduce jamming. An improved interference suppression scheme is desired.